1. Field of the Disclosure
The present disclosure generally relates to bearings, and, more particularly, to hydrostatic and hydrodynamic bearings which use static lubricant pads and a thin film of lubricant, respectively, to support a rotating shaft. Even more particularly, the present disclosure relates to a hybrid bearing having both hydrostatic and hydrodynamic components, where the hydrostatic component is arranged such that the bearing is substantially insensitive to the bending of a rotating shaft supported thereby.
2. Description of the Related Art
Hybrid bearings have been widely used in many applications ranging from machine tool spindles to high-speed turbo machinery, wherein the shafts supported by such bearings are rotated at high speeds. A hybrid bearing is shown and described, for example, in U.S. Pat. No. 5,871,285.
In many bearing applications, a transverse load (in addition to any gravitational effects on the shaft) is applied to the rotating shaft supported by the bearing, thereby resulting in bending or deflection of the shaft. The rotating shaft of a variable displacement vane pump, for example, is subjected to bending. As is known, a vane pump generally includes a rotor having a plurality of radially extending vane slots, a plurality of vane elements slidably-received within the vane slots of the rotor for radial movement therewithin, and a cam having an interior surface coaxially surrounding the rotor so that outer tips of the vane elements contact the interior cam surface during rotation of the rotor. The cam can be pivoted relative to the rotor to charge the extent of eccentricity therebetween and vary the displacement of the vane pump. A variable displacement vane pump utilizing hybrid bearings is shown, for example, in U.S. Pat. No. 5,545,014.
In a single acting vane pump (one inlet and one outlet), a cavity is formed between the cam and the rotor and includes opposing low pressure and high pressure sides. The pump also includes a housing containing the rotor and the cam and having an inlet communicating with the low pressure side and an outlet communicating with the high pressure side. A rotatable shaft coaxially supports the rotor, and the bearings are received in the housing and coaxially support the rotatable shaft. Since the shaft rotates between opposing low pressure and high pressure sides of the vane pump, a transverse load acts on the rotating shaft, causing the shaft to bend or deflect.
Accordingly, there is a need for a new and improved bearing that can be used to achieve higher rotating shaft loads so that machines incorporating such bearing can be built with reduced size and weight, yet provide efficiencies. More particularly, there is a need for a bearing having an increased load carrying capability. Even more particularly, there is a need for a bearing that is substantially insensitive to shaft misalignment caused by deflection of the shaft at increased transverse loads.